Add Chinese+English tts example for flutter (#1192)

@@ -76,6 +76,14 @@ Future<sherpa_onnx.OfflineTts> createOfflineTts() async {
   // modelName = 'en_US-libritts_r-medium.onnx';
   // dataDir = 'vits-piper-en_US-libritts_r-medium/espeak-ng-data';
 
+  // Example 7
+  // https://github.com/k2-fsa/sherpa-onnx/releases/tag/tts-models
+  // https://github.com/k2-fsa/sherpa-onnx/releases/download/tts-models/vits-melo-tts-zh_en.tar.bz2
+  // modelDir = 'vits-melo-tts-zh_en';
+  // modelName = 'model.onnx';
+  // lexicon = 'lexicon.txt';
+  // dictDir = 'vits-melo-tts-zh_en/dict';
+
   // ============================================================
   // Please don't change the remaining part of this function
   // ============================================================